**Subject:** Re: make: needs a tweak

**To:** None *<tech-toolchain@NetBSD.org>*

**From:** Alan Barrett *<apb@cequrux.com>*

**List:** tech-toolchain

**Date:** 04/07/2004 12:17:26
On Tue, 06 Apr 2004, Simon J. Gerraty wrote:
> Expressions like:
>
> echo "${NUMBERS:@n@$n is ${(${PRIMES:M$n} == ""):?not:} prime,@}"
>
> don't work because ${PRIMES} is expanded to nothing before being
> passed to the conditional logic - which insists on having a variable
> reference and so chokes.
This works:
PRIMES=2 3 5 7
NUMBERS=1 2 3 4 5 6 7 8 9 10
foo:
echo ${NUMBERS:@n@$n is ${PRIMES:M$n:C/..*/prime/W:C/^$/not prime/W},@}
> 1. Allow something like:
>
> ${NUMBERS:${PRIMES:S,^,N,:ts}}
>
> Which would be treated as
>
> ${NUMBERS:N1:N3:N5:N...}
This looks powerful enough to be used in very confusing ways.
> 2. Make cond.c not require a variable reference for string
> comparisons. This would allow:
>
> ${NUMBERS:@n@${("${PRIMES:M$n}" == ""):?$n:}@}
>
> to work.
This seems like a good idea.
> 3. Provide a means of saying "don't" expand yet, so that ${PRIMES:M$n}
> could be passed down to cond.c - or perhaps make that implicit if
> :? is present.
Perhaps make backslashes work in ${\${PRIMES:M\$n} == "":?yes:no}
I don't like the idea of making the delayed expansion implicitly
depend on something else in the expression.
> 4. Make:
>
> ${PRIMES:M$n:?:$n}
>
> work as expected? Ie. if ${PRIMES:M$n} is empty, then :? should
> eval false.
This also seems reasonable.
--apb (Alan Barrett)